1. Field of the Invention
The present invention relates generally to security devices, and in particular to a device for coupling an input rotational force with an output shaft.
2. Description of the Prior Art
Security devices are well known and various types have heretofore been designed to restrict access to and use of vehicles, equipment, machinery and other types of property. Among the various types of security devices are padlocks, combination locks, access code security systems and electronic locking devices.
However, even relatively sophisticated security systems are sometimes circumvented. If the protected property has a relatively high value, criminals and others may be motivated to devise methods and equipment to disable or bypass existing security systems.
Security systems generally must strike a compromise between security, i.e. restricting unauthorized access or use, and convenience to authorized users. For example, many motor vehicles have some type of security system, ranging from a simple, keyed locking switch in the ignition system to more elaborate devices which require a user to input a unique access code. However, in spite of the availability of such devices, vehicle theft remains a major crime problem. Cost, of course, is another significant factor since equipment manufacturers and owners are reluctant to add expensive security systems to their equipment and must be convinced that the likely benefits, i.e. preventing theft losses, outweigh the added expense.
A related crime problem involves the theft of construction equipment, including earthworking, excavation, material-handling and paving equipment. One reason that construction equipment is stolen so frequently is that, compared to its relatively high value, it is often relatively easy to steal. For example, on many construction sites, expensive equipment is left unguarded during nonworking hours and can be relatively easily removed. Some construction equipment is so expensive that a thriving criminal enterprise based on stolen construction equipment presently exists. Experience has shown that various ignition switches and mechanical locking devices are easily circumvented by experienced thieves with the proper tools, which are often readily available.
Such widespread equipment theft problems have led to higher theft insurance premiums for construction equipment in general, and particularly the types of equipment that are most commonly considered theft targets.
However, many types of construction equipment include hydraulic systems which, if rendered inoperative, can effectively deter theft. Even construction equipment which is not hydraulically driven can often be effectively secured by placing arms, booms, blades, buckets, etc. in positions that would render it difficult or impractical to remove the equipment. For example, earth moving equipment pieces generally include blades, buckets and the like which can be hydraulically extended or forced against a ground surface. Closing the hydraulic system in this configuration can render removal and transportation of such equipment impractical.
Hydraulic valves are well known, and exemplary valves are shown in the Streun U.S. Pat. No. 2,608,377; Petty U.S. Pat. No. 3,687,414 and Forester et al. U.S. Pat. No. 4,541,608. Such valves, placed at proper locations in hydraulic systems, can be closed to render them inoperative and can be opened for normal operation. Of course, to be effective as a security device, such a valve should be capable of locking in its closed position, which in many valve assemblies involves locking a shaft against rotation.
Therefore, an effective security system should be difficult to circumvent, convenient to activate and deactivate, and relatively inexpensive.
Heretofore, there has not generally been available a security system with the advantages and features of the present invention.